Are there stars and planets between galaxies?
Yes, there are. When galaxies collide, a great many stars (with their circling planets) are cast out of the galaxies. This most likely does not harm the hypothetical inhabitants of those planets in any way, although it does dramatically increase the difficulty of interstellar travel. Clusters of galaxies have a low-level diffuse brightness in visible light caused by all the stars that have been lost from the galaxies and are loose inside the cluster. Outside of clusters, it’s darn near impossible to detect a normal star in intergalactic space. Since all galaxies are built up by collisions, the fraction of stars not in galaxies could be appreciable, maybe 10% (but that’s just a guess).
